The present invention relates to plastic containers for containing fluids under pressure and the methods of producing same and, more particularly, to a one-piece disposable plastic bottle of the champagne base variety having an annular peripheral chime surrounding an inward sloping base portion for containing carbonated beverages and resisting inversion of the base from internal pressure comprising an integral reinforcing ring incorporated into the base and running horizontally in the hoop direction, the reinforcing ring being placed in a location within the base that has a moment arm trying to invert the base and providing sufficient strength to withstand that moment arm and keep the push up of the inward sloping portion intact, to an improved preform for producing such a container, and to the improvement to the method of a blow molding process for producing such a bottle by expanding an elongated preform containing the plastic material for the neck, body and base of the bottle into a mold comprising the steps of forming the preform with annular thickened portions of the preform positioned along the length thereof such that during blowing of the preform the material of the preform will be deposited so that the inward sloping base portion is of a thickness sufficient to resist self-deformation and create a moment arm thereof around the chime tending to unroll and radially stretch the chime and the chime has an integral reinforcing hoop formed therein for preventing unrolling and radial stretching of the chime sufficient to allow inversion of the inward sloping base portion; positioning the preform within a blow molding cavity defining the finished bottle shape; stretching the preform; and, injecting pressurized gas into the preform adjacent the neck whereby the preform is radially stretched outward to fill the cavity and form the bottle from the neck towards the base.
Blow molded plastic bottles have largely replaced the heavier glass bottles previously used for soft drinks, and the like. In a two liter bottle of plastic, the weight of the bottle itself is negligible as opposed to the weight of a glass bottle of similar capacity. The first plastic bottles are generally two piece bottles such as that indicated as 10 in FIG. 1. The bottle 10 comprises the pressure vessel portion 12 and base 14 which permits the bottle 10 to stand upright on shelves, and the like. The pressure vessel portion 12 is typically of a tough, flexible plastic 16 which become resiliently rigid for gripping due to the internal pressure created by the carbon dioxide gas in the soft drink liquid contained therein. The bottom 18 is semi-spherical for the same pressure-containing reasons and, therefore, the separate base 14 is required in order to have the bottle 10 be able to stand by itself. The base 14 is typically of a plastic such as polyethylene and is attached over the bottom 18 of the pressure vessel portion 12 with adhesive.
Presently, approximately 75% of the beverage containers produced worldwide are of the above-described two-piece construction. Because of the inert and non-degradable nature of the plastics used in the plastic beverage bottles and their thin-walled construction, there has been much interest recently in having them recycled rather than deposited in landfills along with other trash. With the increased usage of such plastic bottles, their presence in large quantities in landfills presents a genuine compaction problem. Moreover, the cost of the polyethylene terephthalate plastic employed in such bottles makes recycling a practical alternative to disposal. The two piece bottles, such as bottle 10 of FIG. 1, on the other hand, create recycling problems. First, there are the two different kinds of plastics employed. There is no practical and cost effective way of simply and easily separating the pressure vessel portion 12 from the base 14 so that the two plastics can be processed separately. Also, there is the problem of the adhesive used to fasten the two parts together. The adhesive is a contaminant to any recycled plastic materials.
As shown in simplified form in FIG. 2, the obvious approach to a plastic bottle intended for the holding of carbonated beverages was one such as that indicated as 10' having a so-called "champagne" base 18' which resists the internal pressure. The only problem using a unitary thickness plastic is that the bottom 18' quite often inverts, as depicted in FIG. 3. In an attempt to avoid that problem, numerous bottle configurations have been proposed incorporating integral pressure-resistant ribs, such as those indicated as 22 in FIG. 4, into the bottom 18" of the bottle 10" depicted therein. In this regard, typical prior art approaches to making pressure resistant plastic bottles can be seen with reference to the following U.S. Pat. Nos.--3,511,401 (Lachner); 3,598,270 (Adomaitis et al.); 3,643,829 (Lachner); 3,720,339 (Khetani); 3,881,621 (Adomaitis); 4,108,324 (Krishnakumar et al.); 4,134,510 (Chang); 4,334,627 (Krishnakumar et al.); 4,403,706 (Mahajan); 4,467,929 (Jakobsen et al.); 4,525,401 (Pocock et al.); 4,249,667 (Pocock et al.); 4,254,882 (Yoshino); and 4,261,948 (Krishnakumar et al.). Another prior art reference, U.S. Pat. No. 4,177,239 (Glittner et al.), relates to a two step blow molding process in which first and second blowing pressures are utilized.
As is well known to those skilled in the art, simpler is better when it comes to blow molding a bottle design and while the various rib patterns generally work in preventing bottom inversion, they create a multitude of problems with respect to a consistent and cost effective blow molding process for their production.
Another aspect of plastic bottle production by blow molding techniques which is known in the art is the use of varying wall thicknesses at critical points of stress, such as in the neck and capping threads. A good example of such a prior art approach and the apparatus employed therewith can be seen with reference to U.S. Pat. No. 3,137,748 to Makowski. FIGS. 5-7 hereof depict the process and apparatus of Makowski in simplified form. As shown in FIG. 5, a double two-part mold 24 is used to create a preform 26 of the plastic to be used for the bottle. The mold 24 has a neck-producing portion 28 and a bottle-producing portion 30. A hollow core pin 32 is inserted into the assembled mold 24 and the preform 26 mode by injecting the plastic through a sprew hole at 34. The bottle-producing portion 30 of the mold 24 must be a twopart or split mold since the core pin 32 is cylindrical and the preform 26 contains areas of various thickness to provide additional material for various areas of the finished bottle.
As shown in FIG. 6, the preform 26 with the core pin 32 therein and the neck-producing portion 28 of the mold 24 in place is removed from the bottle-producing portion 30 following the injection molding procedure and mounted to a blow mold 36 having a bottle-defining cavity 38 therein. As known by those skilled in the art, various considerations relative to the temperature of the preform prior to the actual blow molding step must be accounted for. For purposes of the present discussion, however, they are of no real importance and, therefore, will not be considered. The core pin 32 of Makowski is hollow and contains an integral valve (not shown) at the bottom end thereof. With the preform 26 positioned within the cavity 38 as shown in FIG. 6, the valve is opened and pressurized air 40 injected causing the preform 26 to stretch outward from the bottom up, as indicated by the arrows 42, to fill the cavity 38 and thereby create the final bottle.
The Makowski patent is not directed to producing a pressure-resistant bottle. The variations in thickness of the preform 26 are to provide different amounts of material available for stretching to form various parts of the bottles shown therein which are of complex shape, such as those used for dishwashing liquids and the like. There is no need for the accurate placement of integral reinforcement-producing areas. Moreover, the preform design with respect to the cylindrical core pin 32 makes the use of a more costly and complex two-part or split injection mold for the production of the preform a necessity.
Wherefore, it is an object of the present invention to provide a construction for the bottom or base of a one piece plastic bottle for containing carbonated beverages which is of the champagne type but which resists inversion from internal forces without the necessity of including complex rib structures therein.
It is a further object of the present invention to provide a construction for the bottom of base of a one piece plastic bottle for containing carbonated beverages which is of the champagne type and formed by the blow molding of a preform wherein the preform is of a construction which can be produced in a simple one-part injection mold.
It is yet another object of the present invention to provide a method for the blow molding of a one piece plastic bottle for containing carbonated beverages which has a bottom or base of the champagne type containing integral reinforcing sections accurately and repeatedly positioned during the blow molding process.
Further objects and advantages of the present invention will become apparent from the description contained hereinafter in combination with the accompanying illustrative drawing figures.